In a closing method, a work piece constituted by a metal pipe material is rotated, and while heating the work piece, a die is pressed against the work piece. As the work piece is gradually pressed by the die, the work piece undergoes plastic deformation.
A closing machine used to perform this closing operation comprises an outer diameter chuck that grips the outer peripheral surface of the work piece, and a chuck spindle that drives the outer diameter chuck to rotate together with the work piece. The closing machine closes the work piece by pressing the die, which rotates at an offset in relation to the rotating work piece, against the work piece.
This closing method and closing machine are disclosed in JP2002-153930A.
In this conventional closing machine, the rotary axis of the work piece and the rotary axis of the die are offset from each other in a vertical direction.
However, to modify the offset of the closing operation in this conventional closing machine, an offset adjustment mechanism for raising and lowering the heavy chuck spindle and so on must be provided, causing the structure of the closing machine to become complicated.
It is therefore an object of this invention to provide a closing method and a closing machine with which an offset can be modified easily.